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- Mar 8, 2004
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There's a paper in Nature this week that is full of interesting stuff, including several curve-balls, resulting from a very comprehensive molecular evaluation of relationships between animal groups.
On topic first: molluscs are monophyletic.
Now that I got that out of the way, the non-ceph but most astounding part: Ctenophores (comb jellies) are a separate group from the rest of the metazoans, including sponges. So the metazoa/eumetazoa split is wrong.
In other words, we're more closely related to sponges than to comb jellies. In fact, jellyfish are more closely related to us and sponges than they are to comb jellies.
The article also resolves controversies and validates morphological taxons to some extent: Protostomia, Ecdysozoa, and Lophotrochozoa come out winners, spiral cleavage not so much (in terms of clades, anyway). And the coin "clade A," "clade B," and "clade C" where "clade C" contains our friends the molluscs and clade B, which is a bunch of worms and brachiopods and stuff. Clade C is all the animals that have or whose ancestors had shell-like bits of a certain sort, including mollusc shells. Read the paper if you know/care about these details, 'cause I'm not really qualified to discuss 'chitinous chaetae.' Also, some juggling of the arthropods is described (sorry, Roy, no stomatopods).
The abstract is at
Broad phylogenomic sampling improves resolution of the animal tree of life - Nature
and if you have institutional access, the PDF is at
Broad phylogenomic sampling improves resolution of the animal tree of life - Nature
There's a mainstream science press article that's got some horrible misrepresentation in it here:
Shock: First Animal on Earth Was Surprisingly Complex
but while reading that one, keep in mind that their use of "first animal" is horrible misleading... what they really mean is "last common ancestor between comb jellies and other animals," which was certainly not anywhere close to a "first animal," and shared common traits between apes, octopuses, sponges, and comb jellies, so may not have looked any more like a comb jelly than like an ostrich. Anyway, there were certainly many ancestors leading up to that last common ancestor, and we even know a little about what some (the Edicarian fauna) looked like... like these, for example:
Early life on Earth - no predators, plenty of sex
On topic first: molluscs are monophyletic.
Now that I got that out of the way, the non-ceph but most astounding part: Ctenophores (comb jellies) are a separate group from the rest of the metazoans, including sponges. So the metazoa/eumetazoa split is wrong.
In other words, we're more closely related to sponges than to comb jellies. In fact, jellyfish are more closely related to us and sponges than they are to comb jellies.
The article also resolves controversies and validates morphological taxons to some extent: Protostomia, Ecdysozoa, and Lophotrochozoa come out winners, spiral cleavage not so much (in terms of clades, anyway). And the coin "clade A," "clade B," and "clade C" where "clade C" contains our friends the molluscs and clade B, which is a bunch of worms and brachiopods and stuff. Clade C is all the animals that have or whose ancestors had shell-like bits of a certain sort, including mollusc shells. Read the paper if you know/care about these details, 'cause I'm not really qualified to discuss 'chitinous chaetae.' Also, some juggling of the arthropods is described (sorry, Roy, no stomatopods).
The abstract is at
Broad phylogenomic sampling improves resolution of the animal tree of life - Nature
and if you have institutional access, the PDF is at
Broad phylogenomic sampling improves resolution of the animal tree of life - Nature
There's a mainstream science press article that's got some horrible misrepresentation in it here:
Shock: First Animal on Earth Was Surprisingly Complex
but while reading that one, keep in mind that their use of "first animal" is horrible misleading... what they really mean is "last common ancestor between comb jellies and other animals," which was certainly not anywhere close to a "first animal," and shared common traits between apes, octopuses, sponges, and comb jellies, so may not have looked any more like a comb jelly than like an ostrich. Anyway, there were certainly many ancestors leading up to that last common ancestor, and we even know a little about what some (the Edicarian fauna) looked like... like these, for example:
Early life on Earth - no predators, plenty of sex